The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a method and apparatus for automatically changing a polishing pad in a chemical mechanical polishing system.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly more non-planar. This non-planar outer surface presents a problem for the integrated circuit manufacturer. If the outer surface of the substrate is non-planar, then a photoresist layer placed thereon is also non-planar. A photoresist layer is typically patterned by a photolithographic apparatus that focuses a light image onto the photoresist. If the outer surface is sufficiently non-planar, then the maximum height difference between the peaks and valleys of the outer surface may exceed the depth of focus of the imaging apparatus. It will then be impossible to properly focus the light image onto the entire outer surface.
It may be prohibitively expensive to design new photolithographic devices having an improved depth of focus. In addition, as the feature size used in integrated circuits becomes smaller, shorter wavelengths of light must be used, resulting in further reduction of the available depth of focus. Therefore, there is a need to periodically planarize the substrate surface to provide a planar surface.
Chemical mechanical polishing is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier head or polishing head. The exposed surface of the substrate is then placed against a rotating polishing pad. The carrier provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. In addition, the carrier may rotate to provide additional motion between the substrate and polishing surface. A polishing slurry, including an abrasive and at least one chemically-reactive agent, is supplied to the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate.
Chemical mechanical polishing is a fairly complex process, and it differs from simple wet sanding. In a chemical mechanical polishing process, a reactive agent in the slurry reacts with the outer surface of the substrate to form reactive sites. The interaction of the polishing pad and abrasive particles at the reactive sites on the substrate results in polishing.
Polishing pads used in a chemical mechanical polishing process must be replaced periodically to insure efficient polishing of substrates. In general, pad replacement requires a person to remove a used pad from a platen, to remove excess adhesive remaining on the platen, to place fresh adhesive over the surface of the platen, and to affix a clean polishing pad to the platen.
An additional consideration in the production of integrated circuits is process and product stability. To achieve a high yield, i.e., a low defect rate, each successive substrate should be polished under substantially similar conditions. Each substrate, in other words, should be polished approximately the same amount so that each integrated circuit is substantially identical.
In one aspect, the invention features a method and an apparatus for automatically removing a used polishing pad from a chemical mechanical polishing (CMP) system. A mechanical device is placed against the used polishing pad on a platen in the CMP system, and the pad is chucked to the mechanical device. The mechanical device and the pad are moved toward a used pad receptacle, into which the pad is released from the mechanical device.
Embodiments of the invention may include the following features. A lifting mechanism, such as a pneumatic actuator, may be used to lift the used polishing pad from the platen. A vacuum pump may be used to chuck the pad to the platen.
In another aspect the invention features a method and an apparatus for automatically placing a polishing pad on a polishing platen in a CMP system. A mechanical device is placed against the polishing pad in a pad dispenser, and the pad is chucked to the mechanical device. The mechanical device and the pad then are moved toward the polishing platen, and the pad is released from the mechanical device onto the platen.
Embodiments of the invention may include the following features. The polishing pad may be chucked to the platen. A vacuum pump may be used to chuck the pad to the mechanical device or to the platen. The platen may be aligned at a predetermined orientation as the polishing pad is placed onto the platen.
In another aspect, the invention features a CMP apparatus having a platen adapted to hold the polishing pad, a mechanical device operable to remove the polishing pad from the platen automatically, and a pad receptacle positioned to receive the polishing pad from the mechanical device after the pad is removed from the platen.
In yet another aspect, the invention features a CMP apparatus having a platen adapted to hold the polishing pad, a pad dispenser adapted to house the polishing pad temporarily, and a mechanical device operable to retrieve the polishing pad from the pad dispenser and place the polishing pad onto the platen automatically.
Embodiments of the invention may include the following features. The platen may include a pad chucking mechanism that affixes the polishing pad to the platen. The mechanical device may include a pad chucking mechanism that affixes the polishing pad to the mechanical device. Each of the pad chucking mechanisms may include a vacuum pump. The CMP apparatus also may include a platen alignment mechanism that holds the platen at a predetermined orientation, and a pad alignment mechanism that positions the polishing pad at a predetermined orientation before it is placed onto the platen. A controller may be used to govern the operation of the mechanical device.
In another aspect, the invention features a method and an apparatus for replacing a used polishing pad in a chemical mechanical polishing system. A mechanical device is placed against the used polishing pad while the pad is on a polishing platen, and the pad is chucked to the mechanical device. The mechanical device and the pad then are moved toward a used pad receptacle, into which the pad is released from the mechanical device. The mechanical device then is placed against a clean polishing pad in a clean pad dispenser, and the clean pad is chucked to the mechanical device. The mechanical device and a clean pad then are moved toward the platen, onto which the clean pad is released from the mechanical device.
Advantages of the invention may include one or more of the following. Manual labor may be eliminated from routine replacement of polishing pads. Throughput and efficiency of a chemical mechanical polishing system may be improved, and accidental damage to clean polishing pads during pad replacement may be minimized or even eliminated. Critical alignment between the polishing pad and platen may be controlled automatically.
Other features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized by means of the instrumentalities and combinations particularly pointed out in the claims.